[dataway]

Intake gaskets don't come with the exhaust blockoff I think they did in the old days ... so I made the one in the photo below.

It's about .030" stainless ... no lip that fits under over the exhaust gasket like others I've seen but fits nicely in the opening. Think this will suffice? Might have to tack it in place with some adhesive to get the intake on, but looks like it will work.

I plan on only installing one on the drivers side so the choke stove will still get some heat, but hopefully not roast my intake paint or boil my fuel.

Do you think it will hold up, not burn through around the edges or something.

[surfsama]

I did that on both sides (my carb had an electric choke) with no problems.

The trick is to make sure the plate thickness takes into account the gasket crush depth when you torque-down the intake bolts. You don't what it to be a high point or too low.

[dataway]

It's tad low right now, probably .005-.010" ... wonder what the crush thickness is on these gaskets. Don't want it to rattle around in there either.

[Kenth]

Heat from the crossover channel is one of three factors that helps atomize and vaporize the fuel to a combustible gas.
The other two is velocity and amounts of gas..
If you reduce or take away heat you need to add fuel and rpm´s correspondingly to compensate.
In other words you loose driveability and economy.

This means less or nothing for a race engine running WOT 1/4 miles all day long.

FWIW

[dmac]

Originally Posted by Kenth

Heat from the crossover channel is one of three factors that helps atomize and vaporize the fuel to a combustible gas.
The other two is velocity and amounts of gas..
If you reduce or take away heat you need to add fuel and rpm´s correspondingly to compensate.
In other words you loose driveability and economy.

This means less or nothing for a race engine running WOT 1/4 miles all day long.

FWIW

I thought that keeping the intake cooler helped keep the air cooler and more dense- increasing efficiency. Probably different for where you live, how far you drive, etc.

[Tom Vaught]

Originally Posted by dmac

I thought that keeping the intake cooler helped keep the air cooler and more dense- increasing efficiency. Probably different for where you live, how far you drive, etc.

Most of that BS "benefits"passed on from year to year all disappears when you actually get into it.
Engine needs to have the fuel in a vapor not "rivers of fuel" wandering around on the floor to individual cylinders.

The reason why the calibration needs to be richer is because more fuel is condensing (becoming liquid rivers) on the floor of the intake and not going into the engine as a vapor so the intake charge initially is leaner. Adding more fuel just covers up the poor distribution now in the intake manifold. A choke makes a carb a/f ratio RICHER by taking away air vs the fuel still being metered.

Where you live, how far you drive does make some difference. Even with blocked intake gaskets some heat eventually warms the intake due to "reversion" (exhaust flow back into the intake on every combustion cycle due to a camshaft event called OVERLAP).

But drag racers can see a small benefit because they are running the engine a very short period of time vs any engine driven on the street.

Personally I think the mod is just kidding yourself on any real street car.

Tom V.

[Kenth]

Originally Posted by dmac

I thought that keeping the intake cooler helped keep the air cooler and more dense- increasing efficiency. Probably different for where you live, how far you drive, etc.

Cool air to the carb may be beneficial if calibration is up to it.
The carb and intake though needs the heat for reasons above.

And, it is the temperature of the engine that matters to make a combustible mixture of the fuel, not outside air temperatur,

[Schurkey]

...and is extremely important if the vehicle is driven in cool or cold weather. 'Course, lots of hobby cars never get run when the weather isn't beautiful.

Exhaust-crossover heat makes the engine warm up a lot faster, though.

[shaker455]

Originally Posted by dataway

Intake gaskets don't come with the exhaust blockoff I think they did in the old days ... so I made the one in the photo below.

It's about .030" stainless ... no lip that fits under over the exhaust gasket like others I've seen but fits nicely in the opening. Think this will suffice? Might have to tack it in place with some adhesive to get the intake on, but looks like it will work.

I plan on only installing one on the drivers side so the choke stove will still get some heat, but hopefully not roast my intake paint or boil my fuel.

Do you think it will hold up, not burn through around the edges or something.

[steve25]

On the head side perimeter of that steel I would apply a thin bead of high heat red silicone gasket maker!

The faster you warm up a motor the sooner the running clearances are the way they should and then the least ware will take place, and the fastest way to warm up a motor is to drive it !

[4zpeed]

Originally Posted by Tom Vaught

Most of that BS "benefits"passed on from year to year all disappears when you actually get into it.
Engine needs to have the fuel in a vapor not "rivers of fuel" wandering around on the floor to individual cylinders.

The reason why the calibration needs to be richer is because more fuel is condensing (becoming liquid rivers) on the floor of the intake and not going into the engine as a vapor so the intake charge initially is leaner. Adding more fuel just covers up the poor distribution now in the intake manifold. A choke makes a carb a/f ratio RICHER by taking away air vs the fuel still being metered.

Where you live, how far you drive does make some difference. Even with blocked intake gaskets some heat eventually warms the intake due to "reversion" (exhaust flow back into the intake on every combustion cycle due to a camshaft event called OVERLAP).

But drag racers can see a small benefit because they are running the engine a very short period of time vs any engine driven on the street.

Personally I think the mod is just kidding yourself on any real street car.

Tom V.

Originally Posted by Schurkey

...and is extremely important if the vehicle is driven in cool or cold weather. 'Course, lots of hobby cars never get run when the weather isn't beautiful.

Exhaust-crossover heat makes the engine warm up a lot faster, though.

Originally Posted by steve25

On the head side perimeter of that steel I would apply a thin bead of high heat red silicone gasket maker!

The faster you warm up a motor the sooner the running clearances are the way they should and then the least ware will take place, and the fastest way to warm up a motor is to drive it !

^5 Absolutely agree, thanks for sharing!


Frank

[dmac]

A lot of 'myths' I grew up on are being disproven. Lucky I wasn't emotionally attached to most of them. Even things from 'only' 20 years ago, when I seemed like I was reading everywhere to block of the crossover. . Now the only reason would be to compensate for head/gasket mismatch.

[Tom Vaught]

Hey, if the Gasket Companies could sell you a blocked heat cross-over package vs you using a factory intake gasket, they got your money and you were happy, whether it worked on not. All that rough running had to be from all of that colder air making more power in the engine.

Tom V.

[dmac]

Originally Posted by Tom Vaught

Hey, if the Gasket Companies could sell you a blocked heat cross-over package vs you using a factory intake gasket, they got your money and you were happy, whether it worked on not. All that rough running had to be from all of that colder air making more power in the engine.

Tom V.

Plus I loved the smell of unburned gas in the exhaust and the occasional burst of flames and backfiring from the exhaust when taking my foot off the gas/decelerating.

[dataway]

Wow... I didn't think it would be this controversial. I'm just looking to split the difference between toasting the intake into a rusted mess, vs. ... a few minutes more for the choke to pull off.
Not like I'm going to drive this car to work on a 20 degree day. And I'm not looking for any HP ...

I'm just thinking the system was designed for a daily driver and this is going to be a weekend warrior ... so fast warm up is not a huge issue.

[Kenth]

Originally Posted by dataway

Wow... I didn't think it would be this controversial. I'm just looking to split the difference between toasting the intake into a rusted mess, vs. ... a few minutes more for the choke to pull off.
Not like I'm going to drive this car to work on a 20 degree day. And I'm not looking for any HP ...

I'm just thinking the system was designed for a daily driver and this is going to be a weekend warrior ... so fast warm up is not a huge issue.

You may add the wear factor of running the engine cooler than intended, flushing raw fuel into the cylinders and oil.
This is true for all combustion engines.

[geeteeohguy]

Originally Posted by Kenth

You may add the wear factor of running the engine cooler than intended, flushing raw fuel into the cylinders and oil.
This is true for all combustion engines.

This^^^. Blocking the exhaust crossover on a street driven car is a bad idea if you value engine life. No benefits, only detriments.

[Formulajones]

I'm still wondering if I'm reading this stuff right but.....

I don't believe the heat cross over blocked comment for a minute. I've run them blocked for years without any detrimental affects to engine life. That's just internet mumbo jumbo. Anyone experiencing that are obviously running the carb too fat to begin with. People need a good Wide Band, lol.

I also don't believe the comment that with a removed heat riser, there will be little exhaust heat going through the cross over. That's way out in left field. I've done enough of that testing to know different.

My bird with no heat riser, but an open cross over, will literally cook the paint of the intake of the heat cross over. You can't tell me it's getting very little heat. Plus the fact that the divorce choke still works perfectly??

I also removed the heat riser on my 69Z. The divorce choke on it's aluminum intake works excellent. Fully open cross over on that one. Plenty of heat going through that intake. After running I dare anyone to put there hand on that heat cross over

[Cardo]

So is there room for compromise here? What about blocking one side like Dataway is proposing or partially blocking both to reduce flow? My heads are at SD Performnace waiting in line, and i had full intention of having the crossovers filled - I still think that there is too much heat up there at full temp. I always had problems with my last car with the fuel wanting to boil off. The fuel bowl would be empty the next day after parking the car after a full warm up and drive. I like Dataway's idea but maybe drill a 1/4 inch hole in the middle?

[Tom Vaught]

Originally Posted by Cardo

So is there room for compromise here? What about blocking one side like Dataway is proposing or partially blocking both to reduce flow? My heads are at SD Performnace waiting in line, and i had full intention of having the crossovers filled - I still think that there is too much heat up there at full temp. I always had problems with my last car with the fuel wanting to boil off. The fuel bowl would be empty the next day after parking the car after a full warm up and drive. I like Dataway's idea but maybe drill a 1/4 inch hole in the middle?

If you go to the trouble to have "Piston Aluminum" melted on a crucible and properly filled into a cast iron head cross-over passage then there is a tuning benefit for a race type engine
as now the headers work somewhat better. And of course heat is leaving the engine vs crossing back and forth over the engine when the center cylinders fire. Mod was done in the 70s. With that deal and other mods you can get on average a pretty good 260-270 cfm head for racing. Stock Edelbrock head out of the box will flow similar numbers with no mods and less weight.

But some still like the Old School approach to making power.

Tom V.